One of the barriers to large-scale commercialization of geopolymer binders in the construction industry is the lack of effective admixtutes, particularly retardants, capable of providing longer and more predicted setting times. Retarders are admixtures that slow down the hardening of the cement paste. Retarders commonly used in the Portland Cement industry, such as modified lignosulfonates and carbohydrate derivatives, are generally ineffective when added to geopolymer paste, mortar, or concrete formulations.
To control the setting times of geopolymer pastes, researchers and practitioners commonly use sodium borate decahydrate (i.e., Borax) or sodium pentaborate decahydrate, but results with these retarders are variable. Also, use of more than a few percentage of Borax by weight of the aluminosilicate source is associated with significant reduction in mechanical strength.